Won't it still significantly add to the thickness, at least in terms of making one-handed typing harder?

IME it's pretty comfortable to use.

The sides can be made grippier and the back of the phone left slippery, so the in-out of pocket experience is nice, while the grippier parts fit in the palm when in use.

The added thickness on the border is also a welcome affordance, and as your fingertips are on the thinner back it feels thin still.

To me it's kinda the best of both world.